Receptor Mechanisms 1

Question 1

How can two chemicals do two apparently different jobs?

Answer 1

• Acetylcholine reduces cardiac contraction – less forceful and slows it down
• Acetylcholine increases contraction of the gut (smooth muscle)
• The main difference is what the acetylcholine interacts with.

Question 2

What are the four types of receptors?

Answer 2

• Ligand gated ion channel – fastest receptor
• G-protein coupled protein
• Tyrosine kinase linked
• Nuclear or steroid – slowest receptor as it alters gene expression

Question 3

Describe the ligand-gated ion channel family

Answer 3

Proteins the mediate the superfast responses (receptors)	Agonist/ Ligand that activate the receptors. 
Nicotinic Cholinoceptor	Acetylcholine
5HT3	5-HT
GABAA	γ aminobutyric acid (GABA)
Glycine	Glycine

Question 4

Describe the ion flow of ligand-gated ion channels

Answer 4

Receptor type Ion Membrane potential
Nicotinic (activated by acetylcholine) Na+/Ca2+ Depolarises (more active)
5HT3 Na+/Ca2+ Depolarises (more active)
GABAA Cl- Hyperpolarises (calm down cells)
Glycine Cl- Hyperpolarises (calm down cells)

Question 5

Describe the structure of ligand-gated ion channel

Answer 5

…

Question 6

Describe Myasthenia gravis

Answer 6

• The body creates antibodies that attack the nicotinic receptors that you need for muscle transmission, the receptor becomes degraded, you don’t get the neuromuscular transmission and contractions
• This results in muscle weakness showing droopy eyelids.
• Fatigued
• Difficult swallowing and talking
The muscle nicotinic AChRs become degraded
Targets the alpha 1 subunit
Thus neuronal nicotinic receptors an unaffected
• The reason the ganglionic receptors are not affected (the brains receptors) is because the brain does not have alpha 1 subunit. The body raised antibodies to the alpha 1 but not the other alphas.
• Here the mepps is caused by collisions of the acetylcholine vesicles colliding with receptors and walls of junction.